The invention is directed generally to an enhanced phase detector circuit and, more particularly, to an enhanced phase detector circuit for use in a phase locked loop.
Phase locked loops automatically track fluctuating input signals. FIG. 1 shows schematically a conventional phase locked loop circuit. A voltage control oscillator (VCO) 10 outputs a signal having a frequency controlled by the output voltage from phase detector 12 after it passes through loop filter 20. The phase detector voltage output is amplified and integrated by the loop filter. This causes the VCO frequency to move toward the frequency of the input signal. This process repeats until the VCO frequency equals the signal frequency and the loop is "locked". Phase locked loops are often used for communications applications such as receivers, tone decoders and other types of systems.
In such systems, it is advantageous to have high rates of signal acquisition and tracking and minimal loop slewing. The enhanced phase detector of the invention when utilized in a phase locked loop provides acquisition times and tracking rates an order of magnitude faster than conventional systems. Further, loop behavior does not degrade in the presence of noise which is an important factor when using a phase locked loop in a receiver network.